Smelly (sulfur, like well water smell) in my case was caused by a bacteria in the HW heater. I tried flushing many times but the smell was still there. Finally eliminated it with a cup of Clorox in the HW heater tank, cooked it then let it sit for a few hours. Hydrogen Peroxide should kill the same bacteria.
Not sure why yours is not heating up . . . .
We have 2 thermostats (2 roof AC units) with one of the two controlling the furnace, which runs to the entire coach. Granted, our coach is not even middle end . . . .
Best,
- bob